Genetic modification of oncolytic Newcastle disease virus for cancer therapy.

Clinical development of a mesogenic strain of Newcastle disease virus (NDV) as an oncolytic agent for cancer therapy has been hampered by its select agent status due to its pathogenicity in avian species. Using reverse genetics, we have generated a lead candidate oncolytic NDV based on the mesogenic NDV-73T strain that is no longer classified as a select agent for clinical development. This recombinant NDV has a modification at the fusion protein (F) cleavage site to reduce the efficiency of F protein cleavage and an insertion of a 198-nucleotide sequence into the HN-L intergenic region, resulting in reduced viral gene expression and replication in avian cells but not in mammalian cells. In mammalian cells, except for viral polymerase (L) gene expression, viral gene expression is not negatively impacted or increased by the HN-L intergenic insertion. Furthermore, the virus can be engineered to express a foreign gene while still retaining the ability to grow to high titers in cell culture. The recombinant NDV selectively replicates in and kills tumor cells and is able to drive potent tumor growth inhibition following intratumoral or intravenous administration in a mouse tumor model. The candidate is well positioned for clinical development as an oncolytic virus. IMPORTANCE Avian paramyxovirus type 1, NDV, has been an attractive oncolytic agent for cancer virotherapy. However, this virus can cause epidemic disease in poultry, and concerns about the potential environmental and economic impact of an NDV outbreak have precluded its clinical development. Here we describe generation and characterization of a highly potent oncolytic NDV variant that is unlikely to cause Newcastle disease in its avian host, representing an essential step toward moving NDV forward as an oncolytic agent. Several attenuation mechanisms have been genetically engineered into the recombinant NDV that reduce chicken pathogenicity to a level that is acceptable worldwide without impacting viral production in cell culture. The selective tumor replication of this recombinant NDV, both in vitro and in vivo, along with efficient tumor cell killing makes it an attractive oncolytic virus candidate that may provide clinical benefit to patients.